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Discussion Starter #1
Hi Guys,



Anyone who read my other posts knows that i have just been through the ringer on rebuilding my 89 TW. I had the top end redone. Replaced all my seals honed cylinder, new piston and rings, new valve seals, new exaust valve and had the machine shop do a valve job. So now my engine runs fine and i have ridden it about 20 miles since i re-built it. But it smokes like crazy is this normal and if so how long can I expect it to last ? Any help or suggestions are greatly appreciated.



-Josh-
 

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Motors are not suppose to smoke! Even if it has just been rebuilt. I'd say you got yourself a problem. Oil is getting into the combustion process somehow. Could be a lot of different problems.
 

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Your running regular dino oil in that rebuild right? Semi or full synthetic oil in a new or rebuilt engine is a no/no.



Are you still running stock piston and ring sizes or did you go up to 1st oversize?



What's your compression psi? Stock is listed at 128psi



What does your plug look like?







There's always the ever telling leak down test ...



http://www.dansmc.com/leakdown.htm



Or



http://www.motorcycl...t/leakdown.html
 

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Discussion Starter #4
Your running regular dino oil in that rebuild right? Semi or full synthetic oil in a new or rebuilt engine is a no/no.



Are you still running stock piston and ring sizes or did you go up to 1st oversize?



What's your compression psi?



What does your plug look like?







There's always the ever telling leak down test ...



http://www.dansmc.com/leakdown.htm



Or



http://www.motorcycleproject.com/motorcycle/text/leakdown.html
i am running stock piston, i havent tested the compression but can tomorrow and the plug was a medium tan color. And yes im using yamalube 10w20
 

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If your plug is tan and not oily I'd suspect valve seal.



Take off the header and take a peak inside at the exhaust valves. If they cut the valve seats with an arbor-guided cutter it could have taken out the seal if debris got in there.



And take off your valve cover and scope out if the seal is seated and its overall condition.
 

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hmm.



Did the cylinder get measured to make sure it's still within specs for a stock sized piston/rings?



Wear limits are in the down loadable tw shop manual but I have time to type a couple here.



Cylinder bore measuring point from top 66.97-67.02mm or 2.637" to 2.639"



Cylinder bore wear limit 67.10MM or 2.642"



Some sage advice I've read and benefited from. Link



Take the piston measurement and subtract it from the cylinder measurement. Compare the result with the piston clearance given by the manufacturer of the piston. If it is within that specification you could hone the cylinder and put in a new set of rings. If it is OVER that specification you will need to bore the cylinder out to the next biggest oversize and buy a new piston and rings.



Cheap hones will brake the glaze but not much more. At least if you try to do more you are in for a real fun time. The problem is that you can't hold the taper and out of roundness with any kind of accuracy. This is not to say this can't be done, just that it is very hard to do.



Everybody seems to think a new set of rings should cure everything. I wish it was true... but it's not ! I would say 95 % of the time, especially on a dirt bike, you will need to bore it oversize. Sometimes, on a big street bike, the pistons will be within spec, but on most of the dirt bikes you are going to have to bore it.





Other TW honing posts



http://tw200forum.com/forums/62396/ShowPost.aspx



http://tw200forum.com/forums/77543/ShowPost.aspx





 

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Discussion Starter #7
hmm.



Did the cylinder get measured to make sure it's still within specs for a stock sized piston/rings?



Wear limits are in the down loadable tw shop manual but I have time to type a couple here.



Cylinder bore measuring point from top 66.97-67.02mm or 2.637" to 2.639"



Cylinder bore wear limit 67.10MM or 2.642"



Some sage advice I've read and benefited from. Link



Take the piston measurement and subtract it from the cylinder measurement. Compare the result with the piston clearance given by the manufacturer of the piston. If it is within that specification you could hone the cylinder and put in a new set of rings. If it is OVER that specification you will need to bore the cylinder out to the next biggest oversize and buy a new piston and rings.



Cheap hones will brake the glaze but not much more. At least if you try to do more you are in for a real fun time. The problem is that you can't hold the taper and out of roundness with any kind of accuracy. This is not to say this can't be done, just that it is very hard to do.



Everybody seems to think a new set of rings should cure everything. I wish it was true... but it's not ! I would say 95 % of the time, especially on a dirt bike, you will need to bore it oversize. Sometimes, on a big street bike, the pistons will be within spec, but on most of the dirt bikes you are going to have to bore it.





Other TW honing posts



http://tw200forum.com/forums/62396/ShowPost.aspx



http://tw200forum.com/forums/77543/ShowPost.aspx
Im not sure how they did the valve seats.I had the machine shop put in new viton valve seals and do the hone on the cylinder.Gave them a copy of the manual at there request so i am hoping they measured everything as they did tell me that a standard piston was what i needed. Before i re-assembled it i did blast the intake and exaust valves with WD-40

and also the old valve seals were gone and it smoked before im wondering it it could be oil burning out of the exaust or WD-40 burning off the valves.
 

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Im not sure how they did the valve seats.I had the machine shop put in new viton valve seals and do the hone on the cylinder.Gave them a copy of the manual at there request so i am hoping they measured everything as they did tell me that a standard piston was what i needed. Before i re-assembled it i did blast the intake and exaust valves with WD-40

and also the old valve seals were gone and it smoked before im wondering it it could be oil burning out of the exaust or WD-40 burning off the valves.


Any left over oil will burn off within 5 miles of riding, so I doubt that is the issue, unless all you did was start it up and shut it off right away.
 

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Discussion Starter #9
Any left over oil will burn off within 5 miles of riding, so I doubt that is the issue, unless all you did was start it up and shut it off right away.
i checked my valve clearences and tried to do a compression check but no joy as i dont have the right adaptor for this size plug hole it seems as it smokes less today im wondering if its just going to go away
 

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i checked my valve clearences and tried to do a compression check but no joy as i dont have the right adaptor for this size plug hole it seems as it smokes less today im wondering if its just going to go away


Check your oil level. Make sure it's not going away because you don't have oil left to burn.
 

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Bad valves seals tend to smoke on start up and clear after a few minutes.



Bad rings tend to smoke when you give it throttle.



But give it time (50-100 miles if it's not too bad) for the new rings to bed in to the honed cylinder, before you tear it apart again.



When you do a compression test if you have a newer CV carb take it off first, if you have the older slide carb, keep the throttle wide open while cranking the engine. You must allow full air flow for an accurate reading.

Sorry if you already know all this, but it may help other who don't.
 

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Are you sure you gapped and indexed your rings properly. If not it can allow excessive oil to get in the combustion chamber. Happened to a friends quad after he rebuilt it. Smoked like a freight train.
 

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Discussion Starter #13
Are you sure you gapped and indexed your rings properly. If not it can allow excessive oil to get in the combustion chamber. Happened to a friends quad after he rebuilt it. Smoked like a freight train.
yes i offset the rings as per the manual is anyone sure of the measurement of the plug hole so that i can get the correct fitting to do a compression test
 

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Discussion Starter #15

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Discussion Starter #16
Well I got home from work today and I had trouble starting her up. So I took the airbox off the carb and noticed it looked like it was popping through the carb. Then I noticed it was coming from the air-box when I got it started.I proceeded to unhook the breather hose from the air-box and let it run. Then I Noticed when I rev it up I was getting exaust puffs through the breather and it was always blowing air.I am guessing that this is not supposed to happen so I now beleive my problem to be the piston/rings. I dont know if i should run it like this, or just get ready to tear down again?



-josh-
 

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Discussion Starter #18
Please explain how a problem with piston and/or rings can force exhaust past an intake valve.
it is not popping through the carb im sorry i must have not written that clearly enough

it is however blowing out from the crankcase ventilation hose
 

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Yes, bad rings will cause smoke from the breather, but so will overfilling with oil.

A little air pulsing through is normal, this gets more as you rev higher.

Shouldn't smoke though.
 

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Discussion Starter #20
Bummer looks like im going to have to tear her down again. Hope it stops raining here soon so i can get it done before it starts snowing.
 
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